A gas turbine engine is generally mounted to a pylon that is attached to an aircraft frame of an aircraft. Engine mount systems incorporate a backup system that provides a redundant secondary load path if a primary load path fails. The secondary load path is not engaged under normal load conditions or limit maneuver load conditions. In one example, the backup system includes a waiting link having a gap provided at the bottom of the waiting link that prevents engagement of the secondary load path.
For an aft engine mount, the waiting link is positioned between two primary links. In one example, the waiting link is located between the V3 and V2S4 links. If one or both of the primary links fails, movement of the gas turbine engine closes the gap at the bottom of the waiting link to engage the secondary load path. The engagement of the waiting link is not detected until the aircraft is visually inspected
When the waiting link is engaged, vertical loads will move the gas turbine engine upwardly or downwardly, and a substantial vertical load can bottom out a ball bearing at either a top location or a bottom location of the waiting link. The kinetic energy associated with this movement could result in an impact force that is higher than the design load. A dynamic amplification factor is applied to the static load, as well as the fatigue spectrum, to ensure the lug joint has adequate capability.